Containers blow molded from linear high density ethylene polymers are easily fabricated at modest cost and have received wide public acceptance as containers for many types of liquid products, including distilled water, aqueous hypochlorite bleaches, vinegars, cooking oils, lubricating oils and the like. Such containers also have been used for packaging of certain types of liquid detergent products. The use of such containers to package liquid detergent products has been somewhat restricted, however, by reason of the fact that many types of liquid detergent products accelerate the tendency of the container to exhibit stress cracking. Stress cracking is evidenced by the appearance of hazy cracks in the container which are aesthetically unpleasing to the ultimate consumer. In extreme cases, stress cracking can lead to leakage of the contents from the container. The stress crack resistance of linear high density ethylene resins can be improved by blending such resins with other polymers such as butyl rubber, ethylene propylene copolymer rubbers and the like. The resulting blends, however, have reduced strength and stiffness and are not suitable for many packaging applications.
Containers thermoformed (e.g., vacuum formed) from linear high density ethylene polymer sheets also are subject to stress cracking when employed to package certain liquid and solid products, including margarines.
For the above reasons, there is a need in the art for liquid-tight containers fabricated from linear high density ethylene polymers and which have improved resistance to environmental stress cracking. In addition to improved environmental stress crack resistance, such containers will be required to maintain to a substantial degree the desirable physical properties of currently employed blow molded and thermoformed containers prepared from linear high density ethylene polymers.